Impact of micelles on the periodate oxidation of cobalt(II)-trans-cyclohexane-1,2-diamine-N,N,N’,N’-tetraacetate: a kinetic and mechanistic study

The current study intends to investigate the impact of neutral, cationic, and anionic surfactants on the IO₄⁻ oxidation of cobalt(II)-trans-cyclohexane-1,2-diamine-N,N,N’,N’-tetraacetate ([Co^IICYDTA]²⁻). The kinetics of [Co^IICYDTA]²⁻ oxidation in both aqueous and CTAB micellar mediums is determined by quantifying a spike in absorbance at a wavelength of 538 nm, serving as a measure of the concentration of [Co^IIICYDTA]⁻. In the acidic medium periodate ion predominantly exists as octahedral H₄IO₆⁻ ion. The electron transfer reaction involving [Co^IICYDTA]²⁻ and H₄IO₆⁻ proceeds preferentially through an outer-sphere mechanism via the formation of ion-pair. Throughout the range of concentration analyzed, the reaction exhibits first order dependence both on [Co^IICYDTA²⁻] and [IO₄⁻]. The observed constancy in reaction rate within the examined pH range supports the dominant presence of the unprotonated form of [Co^IICYDTA]²⁻ and the single species of periodate ion. The linear increase in oxidation rate with the addition of electrolytes indicates a positive salt effect. The CTAB micellar media facilitates an approximate 2.5-fold enhancement in the rate of [Co^IICYDTA]²⁻ oxidation. TX-100 promotes the oxidation of [Co^IICYDTA]²⁻, while SLS, an anionic surfactant, acts as an inhibitor. The calculated activation parameters further corroborate the suggested mechanistic framework.